A modern tire is known to be formed of numerous elastomeric elements or components with or without internal reinforcement and generally assembled in the green or uncured state.
The said elements generally define two annular packages, of which the first, arranged externally, usually comprises a belt consisting of a number of superimposed tread plies covered externally with a tread, and the second of which, arranged internally, consists of an internal carcass usually comprising an impermeable innerliner, an outer body ply, two metal annular beads with respective outer fillers, two sidewalls, and two abrasion strips, each of which is inserted between the innerliner and a respective sidewall and folded so as to cover a respective bead.
All the aforementioned elements present respective chemical characteristics specially designed to enable each to perform its own specific function as efficiently as possible. Consequently, each of the said elements usually consists of a specific final mix usually formed from a specific masterbatch.
In tire manufacturing plants, each masterbatch is usually formed by means of internal mixers, mainly of the BANBURY type, the chief function of which is to incorporate ingredients, such as carbon black, into the rubber with maximum possible dispersion.
An internal mixer of the aforementioned type is usually employed for mixing relatively heavy batches, each of which is heated as a result of the mechanical action it is subjected to inside the mixer, and then cooled, usually to room temperature, prior to being fed into extruders where it is converted into slabs, strips, pellets or any other suitable form enabling both storage and subsequent processing of the resulting masterbatch.
The aforementioned operations also, obviously, involve heating, as a result of mechanical action, and subsequent cooling.
Each masterbatch is then further processed, usually by means of continuous mixers, to obtain a specific final mix. For this purpose, curatives or crosslinking agents and other chemical compounds are added to the masterbatch to give the said final mix the required chemical-physical characteristics. The final mix is also usually produced in slabs, strips, pellets or any other appropriate form enabling both storage and subsequent processing.
In this case also, the mechanical action the masterbatch is subjected to, for obtaining the final mix, involves at least one heating, followed usually by cooling to room temperature.
Each final mix is then processed mechanically, usually by means of extruders or calenders, to obtain continuous strips, which are usually stored and later subjected, when actually forming or assembling the tires, to cutting operations. Each of the said cutting operations produces, from the said strip, a respective element constituting a portion of a respective tire.
The mechanical processing for producing the said strips also involves at least one heating of the material, usually followed by cooling to room temperature.
Once formed in a known manner, by means of one or more tire building drums, each green tire is usually stored prior to subsequent curing and final inspection.
The above description warrants a number of comments in terms of both cost and functional efficiency.
Firstly, in tire manufacturing plants as of the present, production clearly involves considerable consumption and waste of thermal energy, by virtue of each tire component element being the finished product of a series of processing cycles, each of which involves heating and subsequent cooling.
During each of the said cycles, in fact, the material being processed is brought up to a temperature of usually no more than 120.degree. C., to avoid scorching, and then cooled to room temperature, whereas the finished green tire is brought up to around 200.degree. C. during the curing stage.
Secondly, owing to the relatively large size of the batches treated each time by the said internal mixers, each of the said processing cycles is followed by storage of resulting product. In known plants, this involves not only relatively extensive storage space, with personnel and facilities for controlling and transferring stock, but also a relatively long time lapse between inspection of the finished tire and initial utilization of the base components forming the respective masterbatches. This time lapse, which in relatively extensive known types of plants may be as long as several weeks and even up to one month, may have extremely critical repercussions. For example, a formulation error in the masterbatch of one of the component elements on the tire may only be detected at the finished tire inspection stage, with the result that all the finished tires in which that particular element has been utilized, from that given masterbatch may have to be rejected, and all subsequent batches of the same type and possibly presenting the same error may have to be rejected or recycled.
Furthermore, in known plants of the aforementioned type, storing the various finished and semifinished elements results, not only in inconsistent aging of the elements themselves and, therefore, inconsistent production quality, but also in the green tire having to be assembled at room temperature.